Final answer:
BMP antagonists are expressed in the mammalian node to regulate embryonic development and establish the left-right body axis.
Step-by-step explanation:
In the mammalian node, BMP antagonists are expressed. These BMP antagonists act to inhibit the function of bone morphogenetic proteins (BMPs), which are signaling molecules involved in diverse developmental processes. By blocking BMP activity, the expression of BMP antagonists in the mammalian node helps to regulate embryonic development. For example, the expression of BMP antagonists in the node is crucial for the establishment of the left-right body axis during development.